The National Highway Traffic Safety Administration has performed
research investigating the Test Device for Human Occupant Restraint 50th
male (THOR-50M) response in Oblique crash tests. This research is being
expanded to investigate THOR-50M in the driver position in a 56 km/h
frontal impact crash. Hybrid III 5th percentile adult female (AF05)
anthropomorphic test devices (ATDs) were used in this testing to
evaluate the RibEye Deflection Measurement System. The AF05 ATDs were
positioned in the right front passenger and right rear passenger seating
positions. For the right front passenger, the New Car Assessment
Procedure (NCAP) seating procedure was used, except the seat fore-aft
position was set to mid-track. For the right rear passenger, the seating
followed the FMVSS No. 214 Side Impact Compliance Test Procedure. The
NCAP frontal impact test procedure was followed with additional vehicle
instrumentation and pre/post-test measurements. Results from this test
series were compared with previous NCAP crash tests. The THOR-50M showed
similar kinematics to the Hybrid III 50th but predicted a higher risk of
chest and femur injury. The mid-track seat position of the right front
passenger AF05 led to lower levels of femur compression loading due to
additional distance to the dash. BrIC for the driver and front passenger
showed higher injury risk than [HIC.sub.15]. In all vehicles, the rear
seat AF05 predicted a substantially higher risk of head, neck and chest
injury than the right front passenger. The AF05 RibEye output showed a
higher peak deflection (x-axis) than the chest potentiometer.

The National Highway Traffic Safety Administration's
(NHTSA's) New Car Assessment Program (NCAP) has been conducting
frontal impact tests at 56 km/h (35mph) into a rigid barrier to provide
the public with a simple rating system on the safety of new automobiles
and to aid with purchasing decisions. Currently, a large number of new
vehicles have NCAP star ratings of 4 and 5 stars.

This frontal crash test typifies vehicle crash inputs that are a
major source of injuries and fatalities in the field. Recent Fatality
Analysis Reporting System data indicated that, despite improvements in
seat belts and air bag technology, restrained occupant fatalities
persist in frontal impacts.

This NHTSA Crashworthiness research study presents results and
compares anthropomorphic test device's (ATD's) response to
that of the most recent NCAP testing. This study utilized new ATDs to
evaluate occupant protection in NCAP's frontal impact crash test.
Test Device for Human Occupant Restraint 50th percentile male (THOR-50M)
were used to determine if current vehicle safety systems can be improved
[1]. The THOR-50M was positioned in the driver's seat.

The Hybrid III 5th percentile adult female (AF05) was positioned in
the right front passenger's seat as it is in current NCAP frontal
impact tests. Since not all passengers sit in the full-forward position,
the seat was positioned at mid-track to investigate the implications for
occupant kinematics and injury risk for smaller occupants.

This study also evaluated the rear seat position because it has
been shown to be less protective for some occupants than the front [2].
An AF05 was used to evaluate the restraint effectiveness for a rear seat
passenger.

Additional instrumentation was added to both AF05 ATDs used in this
study. The RibEye Multi-point Deflection Measurement System [3] was
installed into both AF05s in the hope of enabling improved resolution
for chest deflection. The RibEye system can record up to twelve chest
locations and measure deflections in the local x and y axes.

METHODOLOGY

Frontal Impact Crash Testing

In the NCAP frontal impact test setup, a test vehicle is directed
into a rigid barrier at a speed of 56 km/h perpendicular to the barrier
face. Vehicle instrumentation is comprised of accelerometers positioned
about the vehicle. Based on the response of the ATDs positioned within
the vehicle, an injury risk is calculated for each occupant and those
results are combined to generate the joint probability of injury.

In this study, each AF05s was equipped with the RibEye Measurement
Deflection System to provide greater detail on chest deflection for the
crash events. The instrumentation allows the recording of x and y
positions of LEDs mounted bi-laterally on all six ribs of the AF05. The
LED sensor heads are placed on each rib 6 cm from the center of the
sternum. Rib #1 is at the top of the chest and rib #6 is at the bottom.

In the current research study, six vehicles were instrumented with
additional accelerometers and angular rate sensors to record vehicle
kinematics. In addition, string potentiometers were positioned inside
the vehicle to record the deformation of the left and right side toe
pan. Two Chevrolet Malibu models were tested in sequence to compare ATD
and vehicle response repeatability

Due to the additional ATD and data acquisition equipment, five of
the six vehicles had test weights that were greater than the NCAP
vehicle weights. The single vehicle weighing less was the F-150
SuperCrew which was tested without the 4X4 drivetrain that was present
on the NCAP test vehicle. To assist in bringing two of the test vehicles
(Mazda3, Fit) closer to the NCAP weights, the amount of Stoddard fluid
was reduced to approximately 1/3 of the fuel tank's capacity. Table
1 shows the list of test vehicles and corresponding NCAP vehicle tests.

RESULTS

Injury Criteria and Associated Injury Risk - THOR-50M

Occupant injury risk was assessed by determining the probability of
a given severity of injury based on the Abbreviated Injury Scale (AIS)
[4] [5]. For the head, neck, and chest, the probability of an AIS score
of three or higher (AIS [greater than or equal to] 3) was calculated.
For the femur, the probability of an AIS score of two or higher (AIS
[greater than or equal to] 2) was calculated. The injury criteria and
associated risk functions used to predict injury risk for the THOR-50M
in the driver's seat were used in the assessment of THOR-50M injury
in oblique moving deformable barrier crash tests described by Saunders,
et al [6].

Injury Criteria and Associated Injury Risk - AF05

The injury criteria and associated risk functions used to assess
injury for the AF05 in this right front passenger seat were those used
in frontal NCAP testing [7], with one addition. In this testing, the
front AF05 was equipped with angular rate sensors to allow the
calculation of Brain Injury Criterion (BrIC) [8]. Injury risk assessment
for the rear seat occupant utilized the frontal NCAP risk functions for
the AF05 [7].

Occupant Injury Assessment

Driver

The driver's seat in NCAP tests is positioned at mid-track.
The THOR-50M in this study was seated using a new procedure developed to
achieve reproducible position and posture by accounting for the
adjustability, flexibility, and measurement capabilities of the THOR-50M
[9].

During the tests, seat belt pretensioners and frontal air bags
deployed for the driver. Force limiting seat belts were noted in all
tests at the driver position. However, the Toyota Highlander lap belt
force also showed a rise and peak that is more characteristic of a seat
belt without force limiting. The initial lap belt force indicated force
limiting behavior until approximately 40 milliseconds after impact. The
belt force then steadily increases up to a 6000 lb peak. Seat belt loads
for the driver are shown in Figure 1 and Figure 2.

Curtain air bags deployed in both of the Chevrolet Malibu tests and
in the Toyota Highlander test. Curtain air bag deployment was not
considered to affect ATD response in these test events because occupant
motion was directed primarily forward. In the three tests with curtain
air bag deployment there was no observed contact with the driver's
head.

For all crashes in this study, the THOR-50M [HIC.sub.15] was higher
than the 50th percentile male Hybrid III (AM50) response seen in the
NCAP testing (Table 2). The highest increase over the NCAP results was
seen in the first Malibu test with an increase in risk of 1.1%. This was
also the highest Driver [HIC.sub..15] injury risk for this study

The THOR-50M clearance measurements were compared with the AM50
driver values from similar NCAP tests. In the same seat position, there
was increased clearance between the THOR-50M head and the steering wheel
(Table 3). This additional clearance allowed the THOR-50M head greater
free travel prior to contact with a fully deployed air bag.

With the inclusion of angular rate sensors within the THOR-50M
head, BrIC was also calculated for each test. Table 4 provides the BrIC
value and the injury risk (AIS3+). In all cases, BrIC predicts AIS 3+
head injury risk that is 23 to 47 times greater than that calculated
using [HIC.sub.15]. While BrIC significantly elevates the head injury
risk in the frontal, these BrIC values are lower than the THOR-50M
response seen in oblique testing [6].

The higher biofidelity of the THOR-50M chest resulted in greater
chest deflection (Table 6). The maximum IR-TRACC resultant deflection
within the THOR-50M chest was greater than the maximum chest
potentiometer (chest pot) deflection for the AM50 in NCAP testing. For
each test in this study the THOR's upper right chest quadrant,
opposite the shoulder belt path, showed the greatest deflection.

Injury risk for the THOR-50M was calculated using the Multi-point
Thoracic Injury risk function [6]. The age used in the risk function was
35 years old, which is the age NCAP considers the average for the
driving population for the chest pot risk function [7]. The THOR's
injury risk from chest deflection was at least 10 times greater than the
AM50's risk in similar test events.

The maximum compressive force measured along the z-axis of the
THOR's femur was greater than that of the AM50 test events, yet the
force level did not correlate to high injury risks. Knee air bags were
present in the Malibu and Highlander vehicles.

The difference in knee to dash clearance between the THOR-50M and
AM50 is provided in Table 8 and Table 9. The values within the tables
are the x and z axis differences between the KDL (left knee to dash),
KDR (right knee to dash) measurements from the test setup. Negative
value indicates less clearance for the THOR-50M. The small knee to dash
clearance is also due to the longer THOR-50M femur as well as closer ATD
positioning clearance.

Mazda3 pre-test photos demonstrate the noticeable change in dash to
knee clearance between the two ATDs (Figure 3). The THOR-50M knees are
considerably closer to the knee bolster than the AM50. The z-axis
response of the femur load cell confirms that close proximity of the
THOR-50M knee lead to compressive loading early in the test event.
Output from the femur load cell is initially positive indicating a
tensile force. Knee contact with the dash compressively loads the femur
and results in a negative output value.

Right Front Passenger

The seat position for the right front AF05 in NCAP testing is full
forward. For this study, the right front seat was positioned at
midtrack. Other than this modification, the NCAP frontal impact seating
procedure was used to seat the right front AF05. Compared to NCAP test
data, the clearance between the AF05 chest and the dash increased in all
cases, as did the AF05 nasion to windshield clearance (Table 10).

In all of the tests, seat belt pretensioners and frontal air bags
deployed for the right front passenger. This study's seat belt load
cells indicated seat belt load limiters for the right front passenger.
Shoulder belt load cells showed force limiting behavior at approximately
3,000 N (Figure 4). Lap belt load cell output for all vehicles is seen
as similar except for the Toyota Highlander (Figure 5). In this vehicle,
lap belt force appears to be more similar to the right rear seat
position in the Highlander which does not have a force limiting seat
belt (Figure 12). There was no instrumentation for the right front
passenger belt force in the prior Highlander NCAP test available for
comparison.

Images from test videos showing the right front passenger to air
bag clearance is included in Appendix A. In NCAP tests, frame captures
are collected when the right front passenger contacts the frontal air
bag. A frame capture from the current study at the same event time was
paired to demonstrate the clearance due to the mid-track seat position.
In all cases, the NCAP tests show right front passenger contact with the
air bag occurring earlier than this study due to the seat's full
forward-track position. Vehicle air bags appear to be tuned for the AF05
seated at the full forward-track position.

For the majority of this study's tests, the right front AF05
[HIC.sub.15] head injury risk was low (< 1.1%) as in the NCAP testing
(Table 11). The single test showing higher head injury risk was with the
Ford F-150, with AIS 3+ injury probability increasing from 0.2% to 4.5%.

To investigate the higher [HIC.sub.15] value, video and data was
reviewed from the Ford F-150 crash tests. Head position and timing of
air bag contact is shown in Figure 6 along with the resultant head
acceleration. For the AF05 seated full forward (NCAP), the head fully
contacts the air bag at 48 milliseconds with a resultant head
acceleration of 20 g. For the AF05 positioned at mid-track in the
current study, there is head to air bag clearance at 48 milliseconds
(left image) and head contact with the air bag at 66 milliseconds (right
image). Head acceleration is greater than 40 g at that time point. The
additional clearance to the dash panel due to the mid-track seat
position allows the AF05 head greater free travel prior to air bag
contact, which results in a higher head acceleration value.

The current study's right front AF05 was equipped with head
angular rate sensors which allowed for the calculation of BrIC. The
injury risk calculated for the BrIC measurements is considerably higher
than that calculated from [HIC.sub.15] (Table 12).

NCAP testing performed with a Ford F-150 Super Crew 4X4 pickup
(Test Number 9097) had the right front AF05 instrumented with angular
rate sensors. With the right front seat positioned full forward, a BrIC
value of 0.78 and a 39.4% injury risk was recorded. This risk was over
three times greater than that seen for the AF05 seated at mid-track in
the current study.

The AF05 response showed higher Nij values than NCAP in all but one
test. The largest increase was seen with the Honda Fit with an injury
risk increasing from 6.7 to 11.9% (Table 13).

AF05 chest deflection for NCAP testing is recorded through the use
of a chest pot. The injury risks using maximum chest pot deflection for
the current research study and NCAP tests are given in Table 14. Chest
deflection measured with the AF05 in the mid-track position was higher
in every case than in full forward-track match. However, the percentage
increase in chest deflection was not uniform between tests. Chest
deflection approximately doubled for the Highlander, F-150 and second
Malibu test, while increasing by approximately 50% for the Mazda3 and
the first Malibu test. The Honda Fit test showed a 70% increase in chest
deflection.

In this study, additional right front AF05 chest deflection was
provided by the RibEye Deflection Measurement System (Table 15).
Compared to the chest pot, the maximum RibEye deflection was 7 to 22%
greater in each test. The location of the maximum rib deflection was
consistently at the upper left rib. Appendix B contains tables showing
the maximum rib displacements for the right front passenger in all tests
as well as the maximum chest pot deflection measured.

The compressive femur forces of the current test were markedly
lower than NCAP due to the mid-track seat position and reduced amount of
contact between knees and the lower dash. In this study, the highest
z-axis femur loading was in tension due to inertial loading. Tensile
loading is not used in evaluating injury risk. Table 16 shows the
compressive loading in the current study and the NCAP tests. Compressive
loading is denoted as negative in the femur's coordinate system.

Right Rear Passenger

For this study, an AF05 was positioned in the right rear seat using
the FMVSS No. 214 Side Impact Protection seating procedure. No
supplemental restraint devices (e.g. air bag, seat belt load limiter,
seat belt pretensioner) were present at this seat location in any of the
tested vehicles. In the six crash events there was no significant
contact between the AF05 and the seatback or interior components in
front of the AF05.

The [HIC.sub.15] was calculated for five of the six crash events
(Table 17). Questionable data from the x-axis head accelerometer during
the F-150 test did not allow calculation of [HIC.sub.15]. Head injury
risk ranged from 16.7 to 42.9%.

Chin to chest contact was judged to have occurred in the
Highlander, Mazda3 and Fit tests. In addition to high x-axis head
acceleration peaks (> 70 g) which corresponded with substantial neck
flexion, post-test photos document chalk transfer indicating chin to
chest contact. In the case of the Mazda3, video showed that the right
rear AF05 had the lap belt slide over the top of both iliac crests
(submarining) which induced twisting of the torso with chin to chest
contact. Similar chalk transfer was recorded with post-test photos of
the F-150 right rear AF05; however the head CG accelerometer output was
deemed faulty and is not included as a figure. No indication of chin to
chest contact was noted in either Malibu test. Images from the test
videos for each test showing right rear AF05 torso flexion are included
in Appendix C.

Nij was calculated for each test with a calculated injury risk
range from 21.8 to 36.2% (Table 18).

Chest pot data was collected for each test and presented in Table
19 along with injury risk. The maximum chest deflection and injury risk
was seen in the Toyota Highlander test which had the chest pot bottom
out.

Like the right front AF05, the right rear AF05 had a RibEye
Deflection Measurement System installed. In the Toyota Highlander and
Ford F-150 crash events, the RibEye did not collect data. In each test,
the maximum deformation (x-axis) recorded by the RibEye was greater than
that recorded by the chest pot (Figure 10). The maximum chest deflection
was observed on the ATD's left side but the rib that sustained the
maximum deflection was not consistent. There is not an injury risk
function for RibEye deflections at this time.

The following tables demonstrate the behavior of the RibEye during
the four tests in which the system was functional. Signal drop-out was
noted in each test, with the majority of drop-outs occurring at the left
upper rib (#1), and at the right lower ribs (#5 & #6). The maximum
deflection for each crash test is indicated in bold. If a RibEye signal
drop-out is noted below, the rib deflection prior to signal loss is
provided.

As demonstrated in Figure 8, video of the Mazda3 crash event showed
the lap belt sliding over the top of both iliac crests (submarining) of
the right rear AF05. This explains the belt force behavior for the
Mazda3 shown in Figure 11 and Figure 12.

The anterior superior iliac spine (A.S.I.S.) load cell in the AF05
also provided confirmation of the submarining event. Review of the
A.S.I.S. load cell data which showed a decreasing rate of ilium bone
force of 1,000,000 N/second or more (Figure 13). This instrumentation
response rate was considered by the Japanese New Car Assessment Program
(JNCAP) to indicate a potential abdominal injury caused by the lap belt
sliding off the ilium bone of the pelvis. Such an event would have
reduced the JNCAP abdomen weighed score from a maximum of 3.2 points to
0 points [10]. Currently there is no NCAP injury criterion for abdominal
injury in the frontal impact test.

NCAP Frontal Impact Rating

The NCAP star rating system is based on the combined injury risk to
selected body regions for a series of tests. For the frontal impact
test, the selected body regions are the head, neck, chest and femur.
Individual body region injury risks determined from the ATD response
during the crash test are combined into a joint probability of injury.

The analysis that follows looks at frontal impact test results from
the current study and compares injury risk to prior NCAP tests. These
individual ATD calculations do not take into account the additional NCAP
tests used to generate the Combined Crashworthiness Rating Vehicle
Safety Score.

Joint Probability of Injury, Driver

Table 21 contains the joint probability of injury calculated for
the AM50 in NCAP crash tests. The injury risk was calculated by using
[HIC.sub.15], Nij, and peak resultant chest deflection and peak femur
load in the joint probability of injury equation.

Table 22 provides the joint probability of injury based on the
response of the THOR-50M seated at mid-track in this study. The joint
probability of injury for the THOR-50M is higher compared to the NCAP
tests primarily due to chest deflection recorded by the IRTRACC
instrumentation. Chest deflection is notable for the Highlander, Mazda3,
and Fit leading to a four to seven times greater joint probability of
injury than NCAP tests.

Table 23 is generated for the THOR-50M driver with BrIC substituted
for [HIC.sub.15] for head injury risk in the joint probability
calculation. The head injury risk from BrIC was greater than
[HIC.sub.15] injury risk for each test and contributes to an increase in
all joint probability values. All vehicles show a minimum four times
increase in joint probability of injury over NCAP tests.

Joint Probability of Injury, Right Front Passenger

Table 24 is the joint probability of injury calculated for the AF05
seated full forward in NCAP crash tests.

Table 25 provides the joint probability of injury based on the
response of the AF05 right front passenger seated at mid-track in this
study. The maximum deflection of the chest pot was used for probability
calculations. The Highlander's risk increased by 52% due to an
increase in [HIC.sub.15], Nij, and chest deflection, while the F-150 and
Fit both showed over 80% increase in joint probability of injury
primarily due to an increase in Nij and chest deflection.

Table 26 values were generated for the AF05 right front passenger
with BrIC substituted for [HIC.sub.15] for head injury risk. The head
injury risk from BrIC was greater than [HIC.sub.15] injury risk for each
test and more than doubles the joint probability of injury in the first
Malibu, Highlander, Mazda3, and Fit tests.

If BrIC in the NCAP Ford F-150 test (Test Number 9097) was used to
calculate joint probability of injury for the right front passenger in
that test (Table 24), joint probability of injury increases from 8.4 to
44.4%.

Joint Probability of Injury, Right Rear Passenger

Table 27 provides the joint probability of injury calculated for
the AF05 rear seat passenger. The maximum deflection of the chest pot
was used for probability calculations. High injury risk was noted for
the head, neck and chest leading to a joint probability of injury from
52.6% up to maximum of 86%. The joint probability of injury for the rear
passenger was 3.8 to 6.2 times greater than the front passenger when not
considering BrIC values.

Repeatability of Test Procedure

The repeatability of vehicle response within the current research
study was evaluated by performing two crash tests with the 2015
Chevrolet Malibu. The left and right vehicle frame x-axis accelerometer
data were compared using CORA [11]. CORA software uses two methods to
evaluate the correlation of a signal. The corridor method compares the
deviation between curves while the cross correlation method compares
curve characteristics such as shape, phase shift and size. The CORA
rating in Table 28 compares data from the two 2015 Malibu vehicles in
the current study. The high CORA rating indicates a very high
correlation for vehicle frame acceleration in the two crash tests.

As an additional measure of repeatability, CORA was also used to
compare the current study's two Malibu crash tests to an earlier
2013 Chevrolet Malibu NCAP test (Table 29). The inclusion of a third
test changed the basis for evaluation (corridor, cross-correlation
reference curve) and accounts for the change in rating for the two tests
from Table 28. This evaluation also resulted in a high total CORA
rating.

DISCUSSION

The introduction of the THOR-50M to the NCAP frontal impact test
resulted in an accompanying increase in joint probability of injury for
the driver. While the increase in [HIC.sub.15] was negligible, the
increase in head injury risk was evidenced by the BrIC injury criterion
and associated risk function. The THOR-50M high chest deflections and
greater injury risk was demonstrated using the Multi-point Thoracic risk
function. The maximum resultant deflection was in the upper right chest
quadrant which was opposite the shoulder belt path. The increase in
femur loads was low and did not increase injury risk above 2.2%.

For the front passenger AF05, the joint probability of injury
nearly doubled when BrIC is used for head injury risk for all but one
test. The one exception was the F-150 which increased slightly less than
50%.

The maximum RibEye measurements were greater than those provided by
the chest pot. In the case of the right front AF05, the maximum
deflection was seen at the same rib for each test. This was left rib #1,
in the upper left chest quadrant, opposite the belt path. RibEye channel
drop-outs occurred at the lower right rib for each test event. This was
due to an interruption of the light from the LED unit and has been
reported as due to interference by the abdominal insert or the chest
potentiometer structure [11]. A chest potentiometer was installed in
each AF05 to allow comparison to the RibEye.

The right rear passenger's injury risk was considerably higher
than that measured for the right front passenger where supplemental
restraints, such as pretensioners, load limiters and air bags are
available. A [HIC.sub.15] value in excess of 700 was seen in all tests.
The calculated Nij value was greater than 1.0 for five of the six tests.
Chest pot deflection was double that of the right front passenger. These
three criteria all contributed to a 4 to 6 times greater joint
probability of injury over the right front passenger. Peak shoulder belt
loads for the right rear passenger were nearly double or higher than the
right front passenger. In addition, lap belt submarining of the right
rear passenger was recorded through video and A.S.I.S. load cell output
in the Mazda3 test.

CORA evaluation of vehicle crash pulse for the two Malibu tests run
in series indicated repeatability of the tests. ATD instrumentation
response and injury risks calculated for each seating position were also
similar between tests. For the driver, the greatest difference in injury
risk (5.5%) between the two tests was due to the difference in chest
deflection (3mm). For the right front passenger, the greatest difference
in injury risk (0.8%) between the two tests was chest deflection and
Nij. For the right rear passenger, the greatest difference in injury
risk (3.9%) between the two tests was [HIC.sub.15] (844 vs. 939).

SUMMARY

The THOR-50M in the driver's position for the frontal impact
research tests showed a higher injury risk than the AM50 used in NCAP
tests. The [HIC.sub.15] and femur loads were higher, but the most
significant change to the joint probability of injury was driven by the
chest injury risk and BrIC head injury risk. Chest injury risk and BrIC
more than quadruple the joint probability of injury over NCAP tests.

The repositioning of the AF05 in the right front passenger seat to
mid-track resulted in a notable increase in joint probability of injury
for three vehicles. For the right front passenger, the F-150's risk
increased by 50%, while the Highlander and Fit showed an 80% increase in
joint probability of injury. Maximum deflection of the AF05 chest
potentiometer in this study was greater than NCAP testing. RibEye
deflection was even greater but the percentage increase over the chest
pot was not uniform among the test vehicles. For all of the vehicles,
the inclusion of BrIC head risk at least doubles the joint probability
of injury over NCAP tests.

The AF05 positioned in the right rear seat had higher injury risk
calculated from [HIC.sub.15], Nij and chest compression than the right
front passenger. The joint probability of injury ranged from 3.8 to 6.2
times greater than the front passenger. The maximum RibEye deflection
was greater than the chest pot and there were some RibEye signal
drop-outs during tests. In the Mazda3 test event, video and ASIS load
cell output confirmed the AF05 lap belt slid over both iliac crests and
led to a submarining event.